In rural and remote areas which lack an adequate and accessible water supply, or in areas where water pressure is low, an extra water supply is often necessary when fighting fires. In such situations, a portable water reservoir is useful for storing and delivering water at the scene of the fire.
Upon arrival at the scene of a fire, the portable reservoir is assembled and positioned in proximity to the fire. Water is transported by land and emptied into the reservoir. Depending on the construction of the reservoir, water may be dumped into the top of the reservoir, known as a "dump tank", or may be pumped in through inlet hoses. After filling, fire hoses from a pumper truck are attached to the reservoir and water is pumped directly from the reservoir onto the fire. As the reservoir is emptied, the water is replenished by the water transport system. When the fire has been extinguished, the apparatus is removed from the scene of the fire.
A variety of factors affect the utility and efficiency of a portable liquid reservoir. These factors include the speed with which the portable reservoir can be transported to a desired location, positioned properly, and assembled for use; the rate at which the reservoir can be filled with liquid; the volume of liquid the reservoir can hold; the rate at which the reservoir can be drained of liquid; and, the volume of liquid which can be efficiently removed form the reservoir.
The speed with which a portable reservoir can be transported, assembled and positioned at a desired location depends on its construction and the steps necessary to ready it for use. In the past, portable reservoirs have been constructed as free-standing canvas tanks which require assembly prior to use, or as trailer tanks which require no assembly. The free-standing dump tanks are comprised of a metal or plastic frame and a canvas lining into which large volumes of liquid may be dumped. The free-standing dump tanks are brought to the scene of the fire disassembled or collapsed and are then manually assembled by the fire fighters. The trailer tanks are towed to a desired location, either empty or full depending on their particular construction, and are then positioned as convenient.
The fill rate of a reservoir depends on the size of the opening through which the liquid is to be delivered into the reservoir. This, in turn, depends on whether the tank is of open or closed construction. The fill rate of enclosed reservoirs is slower due to the build up of air pressure within the tank and the limitations on fill rate imposed by the diameter of the fill openings.
The volume of the reservoir obviously depends on its size. Reservoirs may be designed in a variety of shapes and sizes to accommodate the individual fire fighting needs of a fire department.
The rate at which liquid is drained from a reservoir depends on the diameter of the pipes through which the liquid can be drained, the number and size of the openings through which the liquid can be drained, the pumping capacity of the pumper truck, and whether the reservoir is of open or closed construction. The air pressure in an enclosed tank may be somewhat reduced as liquid is rapidly pumped from the tank, thereby reducing the rate at which liquid may be removed.
Finally, the efficiency of a particular reservoir design depends greatly on the volume of the stored liquid which can actually be removed from the reservoir. When liquid is being drained from a reservoir, suction loss is created by the development of whirlpools at the drainage site. When the bottom of the whirlpool contacts the drainage site, suction is interrupted and no more liquid can be removed from the reservoir. The rate of draining liquid from the tank also affects the formation of whirlpools. With many types of reservoirs, a specific volume of liquid contained therein may not be extracted because of the whirlpool phenomenon. This reduces the efficiency of a particular reservoir because it must be refilled more often.
A variety of dump-tanks or other portable reservoirs have been developed to address the considerations enumerated above. U.S. Pat. No. 2,192,593 to Bradley et al., discloses a trailer tank in which the trailer frame itself has been incorporated into the body of the tank. The particular tank disclosed in the patent is a cylindrical enclosed tank designed for land distribution of liquid commodities, similar to tanks used to transport fuels or milk.
U.S. Pat. No. 4,482,017 to Morris, discloses a portable, enclosed liquid supply tank designed to correct the disadvantages of earlier enclosed tanks by including an overflow relief valve and a fill valve. The fill valves or "air holes" are designed to stabilize the pressure between the inside and the outside of the tank when filling or draining. A drain pipe extends from the rear of the tank to allow removal of the liquid. Despite the presence of fill valves and air holes, the rate at which liquid may be removed from the tank is limited by the diameter of the fill valves and the number of air holes. Additionally, the apparatus disclosed in the Morris patent does not provide a method for preventing the development of suction whirlpools, thereby allowing more efficient use of the liquid contained in the tank.
Vinyl of canvas tanks which are assembled at the scene of the fire are also common portable reservoirs. However, these tanks are cumbersome and difficult to assemble. They also have no devices which aid in the prevention of whirlpools, and suction hoses placed in such tanks must have a whirlpool-inhibiting device fitted into the inlet end of the hose. Furthermore, experience indicates that the materials composing these devices are subject to decay if not dried prior to disassembly, and that the tanks must be treated carefully prior to storage and reuse.
Thus, what is needed in the art is a portable liquid reservoir which is formed of a durable material, is easy and quick to assemble, is easily positioned and maneuvered, and allows more efficient use of the liquid contained therein by preventing the development of whirlpools. The present invention solves these problems in the art by providing a portable liquid reservoir that contains anti-whirlpool devices which enable a pumper truck to withdraw virtually every gallon of water before breaking suction; which can be assembled and positioned by one person in less time than supply tanks currently available; and, which can be immediately stored after use without taking any precautions to dry the material and without damage to the tank material.